It was the perfect plan. Strike the Winchester's when they were at their weakest. Their care for one another would always be their downfall and his victory.
From the moment Abaddon had released him from the cage Lucifer had decided to play it smart, this time there would be no announcement of his arrival, there would be no attempt to seduce the youngest Winchester to his side. No this time he would try subterfuge. Though even he had been surprised by just how quickly the opportunity had presented itself, though not in the manner. Dean's prayer had reached every angel on earth, including those fallen from God thankfully for Lucifer.
Of course now he needn't hesitate to reach his vessel, he'd known from the minute he'd arrived back upon the earth that could not risk giving away his true identity so he'd taken on a new one. Ezekial. The angel had been upon the earth keeping a watch over Castiel as he'd tried to aid the Winchester's. Silly loyal Ezekiel, he'd been too distracted with his task of protecting his old commander to notice Lucifer's attack. And as events would transpire, no cover up would be needed. Fate would play it's hand in his favour. If he'd have had any doubt of his father's plan for the great apocalypse the sight of his brothers and sisters falling restored his faith, his deception would not be discovered.
To his detriment he soon learned that even he the devil was not immune from the disaster befalling heaven. His own powers were waning, coupled with the fact that he was not within his true vessel he found himself quickly growing weaker. Time was of the essence. He would not be the first to arrive though, no but with the Winchester's aid he was able to dispatch of his vengeance driven brother, earning his trust somewhat whilst growing more concerned about the rapidly deteriorating state of his current vessel's strength.
It said a lot about the state of the older hunters state of mind that he so quickly agreed to the angel's offer of help, he was always so blind to trusting those who spoke of Castiel with fondness. Within the hour he found himself by Sam's bedside, the sigils around them ensuring that his target would be kept from his siblings clutches – though he presumed it would be Dean they were after to get to Castiel he knew they could use Sam as bait to get their way.
Being under Dean's constant gaze was certainly making his attempts to infiltrate Sam's mind difficult, it took much longer than he would've liked to slip into his mind to see what the current state of play was. What he saw left him troubled. If Sam crossed over with Death for good it would be game over, there would be no way for fate to fix it. The apocalypse would be done. Unacceptable. He needed to be in the vessel immediately. He needed to exploit the Winchester's fear with the lie.
Oh how simple it was to play on Sam's loyalty. He watched on with glee as Dean convinced his brother to accept the dangerous proposal blindly trusting 'Ezekiel' to fix everything and later agreeing to erase his brother's memories of being possessed. What fools. Humanity was such a weak race, how had his father thought them better than his angels. Well, they all soon would learn, he would play the long game. Slowly he would chip away at Sam Winchester till he was in control. And then when the time came he would ensure the battle fate scripted would go ahead. And this time he would be victorious.